1. Field of the Invention
The present invention relates to an antenna device included in a communication apparatus, such as a mobile phone, and a wireless communication apparatus including the antenna device.
2. Description of the Related Art
With recent development of small multi-functional communication apparatuses, such as mobile phones, there have been demands for smaller multi-resonant antenna devices included in such communication apparatuses. An example of an antenna device capable of meeting such demands is disclosed in Japanese Unexamined Patent Application Publication No. 2004-312166.
In this antenna device, a small radiating electrode plate having a feeding conductor plate connected to a feeding unit is disposed substantially parallel to a ground conductor surface, so that a small low-profile device is realized. Then, a pair of short-circuit conductor plates extending from outer edges of the radiating electrode plate is connected to the ground conductor surface. Thus, a first resonance mode based on one of the short-circuit conductors and a second resonance mode based on the other short-circuit conductor are obtained, so that a dual-resonant antenna device is realized.
However, the conventional antenna device described above has the following problems.
If the conventional antenna device described above is small in size, its voltage standing wave ratio (VSWR) tends to be very high at a frequency between two resonance frequencies. As a solution to this, it may be possible to form a matching circuit including chip components such as inductors and capacitors, so as to reduce the VSWR at the frequency between the two resonance frequencies and bring it closer to VSWRs at the resonance frequencies. However, the chip components such as inductors and capacitors have self-resonance frequencies, which are low. Therefore, in an antenna device using high frequencies in the ultra-wideband (UWB) and having resonance frequencies as high as 3 GHz or more, it is difficult to form a desired matching circuit from chip components.